The invention relates to coating apparatus, and in particular to an improved rotary atomizing apparatus for depositing coating material on a workpiece.
Rotary atomizers for applying coating materials such as paint onto articles are known in the art. Conventionally, such a device comprises a rotary bell atomizer carried on an output shaft of an air driven turbine, a rotor of which rotates the shaft and bell. The bell is rotated at high speeds, normally between 4,000 and 60,000 rpm, and paint delivered to a paint feed surface of the rapidly rotating bell is discharged from a peripheral edge of the bell in an atomized spray of small paint particles. The bell is charged to a high voltage, often between 30 KV and 120 KV, to electrostatically charge the paint particles, and the article is grounded, so that the charged paint particles are electrostatically attracted to and coat the article. Usually, a curtain of shroud air flowing around the rotary atomizer aids in shaping the pattern of atomized paint particles and in moving the particles toward the workpiece.
Rotary bell atomizers ordinarily include a front cup-shaped member having a forward paint feed surface across which paint travels to a peripheral discharge edge. Rearwardly of the cup-shaped member is a housing that defines, along with the member, a paint cup on the back side of the member, into which paint is introduced for flow through passages in the member to the forward paint feed surface. During color changes and when the atomizer is to be left idle for a period of time, flush is introduced into the paint cup to clean the atomizer of paint. Nevertheless it sometimes happens that an operator will forget to flush the atomizer when it is to remain idle, with the result that paint dries in the paint cup. Once the paint dries, it cannot readily be removed with flush, so to unclog the atomizer and prevent contamination of subsequent colors of paint, it must be disassembled for manual cleaning. However, conventional rotary atomizers cannot conveniently be disassembled.
In addition, air driven turbines of such coaters are usually located well rearwardly of the atomizer bell, so that the rotor of the turbine is required to turn the bell through a shaft. The arrangement requires a number of often troublesome rotary seals around the shaft between the rotor and bell to prevent paint in the paint cup from flowing back to the turbine. Further, air for driving the turbine is, after use, simply exhausted to atmosphere and wasted.